1. Technical Field
The present invention relates to a projection optical system suitable to be incorporated in a projection image display device for projecting an image of an image display element in an enlarged manner, and the projection image display device equipped with the projection optical system.
2. Related Art
The optical system, which can be incorporated in a projection image display device such as a projector, is described in JP-A-2014-29392. When incorporated in projection image display device, the optical system in this document forms an intermediate image of the image of the image display element inside the optical system to reimage it on a screen. Specifically, the optical system of the document is provided with a first lens unit for making the screen (a enlargement-side imaging surface) and the intermediate image conjugate with each other, and a second lens unit for making the intermediate image and a reduction-side imaging surface (the image of the image display element) conjugate with each other.
In the projection optical system, it is required to enlarge the field angle so that the image of the image display element can be projected in an enlarged manner even in the case of disposing the projection image display device at a position close to the screen. However, if the field angle is enlarged, a distortion becomes apt to occur on the projection field projected on the screen. Regarding such a problem, it is possible to suppress the distortion of the projection field by increasing the number of lenses constituting the optical system. However, if the number of lenses increases, there arises a problem that the total length of the lenses increases.